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Another wild-hair thought.... will this work??..

What if I use the bike's tranny for all of the 'normal' shifting duties, but put a small, light manual car tranny 1/2 way down the driveshaft to give me reverse and 'overdrive' (using it's 5th gear)?..

The car tranny (rear wheel drive) would have no clutch/bellhousing.. it would just be a u-joint in and a u-joint out.. In my tiny brain, it seems it would work if you only ever shifted the car tranny while stopped.. For example, you'd basically leave the car tranny in 4th gear (1 to 1 forward ratio) almost all the time (remember, the 'normal' shifting duties are performed by the motorcycle's internal tranny)... ocassionally you'd shift the car tranny into reverse when needed (back up, stop, then shift it right back into 4th gear to get your 1 to 1 forward ratio back).. and if ever you knew you were going on a freeway trip, you could put the car tranny into 5th gear (overdrive) before you took off on your way.. Best idea ever, right

There is an issue trying to shift a manual car tranny without a clutch, but again- if you did all of your (car transmission) shifting at a standstill, could you not coax/force the shifter through it's travel? There's also a weight penalty, but maybe you could remove the car tranny's unused 2nd and 3rd gears for some weight savings?

If this could be made to work, maybe you could plan for your car tranny's only forward gear to be overdrive (5th gear), which would allow you to take out 2, 3 AND 4th gear (more weight savings), and maybe then use a rear differential that would have eluded you before due to gearing (i.e. a Miata IRS diff with it's 'undesirable' ratios)?? But wait, there's more! If you (ok, this is all about me..) could use that Miata diff (because I'm now in 'constant' overdrive), I could save so much weight using it (Miata Diff) instead of the Ford 7.5 diff I have now, that I could conceivably come out 'even' on my aformentioned weight penalty!?!!?

Solved the puzzle, didn't I?!?



Alright, go ahead and tell me it can't be done..

Strip me of my dreams and reason for living- I can take it...


-ccrunner

It has been discussed before but I could not find it. I suggested using a Samurai trans because it is very light. I don't remember what was said but I don't think anybody poop poohed it. I think it would be a cheap way to go. Russ

I have thought about the same thing so I am interested in what those who have actual experience with drivetrains have to say.
I agree it would be a good way to have multiple gear options for auto-x, track days or racing, road, and highway, with the added bonus of reverse!

I had thought of using an air cooled VW transaxle as that would eliminate the separate diff but they have become quite expensive since I built my last one 22 years ago. I have not been able to find a used one here either.

My main concern would be the torque at the input shaft to the transmission. Sport bikes don't make a ton of torque but there is usually approximately a 2:1 reduction between the crank and the transmission then whatever the transmission ratio may be. With a roughly 3:1 first gear, that wimpy 40-50 ft-lbs at the crank becomes 240-300 ft-lbs at the transmission output shaft. A light weight transmission from a low power vehicle may not be able to handle it.

Regarding shifting, it would be no different than shifting without a clutch. As you let off the gas put light pressure on the shifter, let it pop into neutral when the RPM is right, tap the gas to rev match, put a light pressure on the shifter in the direction of the next gear, and when RPMs match it will pop into place.

I wonder if our very light cars (1200-1500lbs) will let us get away with the extra torque going into the car tranny.. I would think so...

I love the idea of picking up a 'reliable' reverse this way, not to mention the ability to fine-tune the ratio you want to run at a given place/time by simply shifting the car tranny by one gear

I want to avoid making this any more complex than needed, but this approach does seem to have some merit.. I hate the idea of adding a 53lbs tranny (Samurai) to the mix, but doing so would allow me NOT to run an electric reverse setup (aprox 10-15lbs), and it could even have me ditch the 7.5 IRS diff (aprox 65 lbs) and run a Miata diff (weight unknown, but it's less by 10-15lbs methinks).. My math shows a BEC could run a stock Miata diff (3.9) with the Samurai tranny in 5th gear (.795), giving the car about a 3.1 final ratio for those 'freeway' days..

-ccrunner

I have an ideal to do the overdrive and the reverse and will begin puting things together. I guess the demand is for a reverse gbox /w OD verses a simple reverse box

Did some more digging and found this old thread if it's of any use to anyone...

http://www.locostusa.com/forums/viewtop ... feb1ee3b2c

I've put quite a lot of thought into this setup and am strongly considering heading this way for my build (or at least package protecting for it). Some considerations:

1. The car trans needs to be sized based on the tractive effort of the vehicle more than the output torque of the bike/bike trans combo. The maximum bike sprocket output torque would destroy anything but a huge car transmission if it could put the power down. With the primary reduction plus first gear on the bike trans you are looking at 400+ ftlbs at the input shaft to the car trans with a naturally aspirated 'busa. Add to that that the 4th and 5th gear sets in the car trans are not designed for the huge inertia loads of a fast clutch launch. Further, you may want a turbo which puts your input shaft torque up in the 600's.

However, the wheel torque for 0.9G accel (which includes a nice padding, I think 0.65G is more reasonable) is ~900-1000 ft-lbs. Pass this forward through a ~4:1 rear diff and you have an output shaft torque of ~250 ftlbs. In 4th gear this equals your input shaft torque and seems entirely reasonable. I don't think it's Suzuki Samurai reasonable but it's at least garden variety T5 reasonable.

2. Lash - I don't know how to figure this one out besides to build it. The sequential bike transmissions don't like a lashy driveline (think loose chain) and I don't know how much the car trans would introduce. Also, the car trans may not like the hammering it would get from the shifting going on upstream. Nice part is that if the experiment fails you can always take it out and be back to a normal BEC driveshaft.

3. Shifting/clutch - Just put the bike clutch in, same difference basically. All you need to do is disconnect the engine from the wheels.

4. To get down to something similar to the bike gearing when in OD you need an "american style" overdrive of <0.7:1 Do the math on most import manuals and you will find 0.8-0.9 much more common and not really worth it IMHO. T5's came with 0.67 in many applications.

5. Removable bellhousing makes packaging much easier, another win for the T5.

6. Mass - Best I can calculate for a no-bellhousing T5 with first, second and third gears removed is only ~45lbs, totally worth it.

7. 944/audi trans is also interesting, just put it in place of your diff and gut gears 1 2 and 3. Would just poke out the back and they are big $$ with a limited slip (dirt cheap without). It's a little hard to find the right ratios so you don't have a normally geared BEC with an underdrive but they do exist (some mid 80's 924's came with 3.83 and you can swap in an audi 0.7 5th gear)

I'm sure there's more but that's what I remember right now. I have a nice simulated car in solidworks and lapsim but no metal sitting on a table yet, soon I hope.

Alex

All very thoughtful Alex.. I hadn't even thought about how you could seemingly just use the bike clutch and shift the car tranny- you're right, all the tranny wants is to be 'disconnected' to be able to shift, and it shouldn't matter if that's taking place in a bell housing or in a MC gear case.. Which leads me to wonder if you could use your T5 tranny as intended by leaving the bike tranny in 6th (1 to 1), using the bike tranny's clutch, and shifting the T5 as your project's 'primary' transmission??- could the bike tranny take hard launches in 6th gear (while downstream the T5 is in 1st gear...).. As for drivetrain lash- I wonder about that too.. maybe a guibo could soak it up?

Love love love the idea of an overdrive at .6 or .7 to 1

-ccrunner

My mate who races Clubmans in Oz has his 5 speed Corolla gearbox pared down to 10kgs/22lbs, here is a picture of how much he shortened it by ..

Wow, he really went at it! Once your good enough to do that, I suppose everything just looks like raw material!.

It would be nice to have both boxes and choose which one you wanted to shift (except for the weight). Right now my GSXR with a 3.933:1 rear end ratio ends up with all of my 6 gears being spaced between the motorcycle's normal 1st and 2nd only. The bike has a larger dia tire and the sprocket ratio is 2.47:1. But if you like really close ratio gears it's OK considering that you have 12,400 RPM to work with.

But it sure needs a higher gear for cruising. That's where leaving the bike box in 6th and using the car box would be nice. Hmm, let's see, 6 gears & 5 gears, YEAH that's what we need THIRTY SPEEDS FORWARD AND 6 IN REVERSE!

Yashuatwo is putting an overdrive in the reverse box he is making. I think he might be using motorcycle gears in it. He has a thread so you can look up his progress.

Another option is a DNE2 'overdrive' transmission unit. Del Long is using one as 2 speed transmission in his new E-Mod car and it has reverse. From what I remember him telling me, there's a quickchange gearset in it to set gearing in the other 'gear', as the 1 is a straight through ratio. I'd imagine you could find a ratio that would be good for the highway, and use the 1:1 for around town, plus still have reverse.

--JOsh

Anyone have a link/info on a DNE2 box having reverse? I Googled it and found Doug Nash Engineering/US Gear OD info (both once produced an OD box, but no longer).. but no mention of this overdrive unit having reverse.. also couldn't get a good link to Del Long's jeep/ e-mod build that seems to be using the DNE2.. Any info/links would be appreciated...

ccrunner